An alternating-current surface-discharging panel representative of a plasma display panel (hereinafter abbreviated as “panel”) has a large number of discharge cells formed between the front plate and the rear plate faced with each other.
For the front plate, a plurality of display electrode pairs, each made of a scan electrode and a sustain electrode, are formed on a front glass substrate in parallel with each other. A dielectric layer and a protective layer are formed to cover these display electrode pairs. For the rear plate, a plurality of parallel data electrodes are formed on a rear glass substrate and a dielectric layer is formed over the data electrodes to cover them. Further, a plurality of barrier ribs are formed on the dielectric layer in parallel with the data electrodes. Phosphor layers are formed over the surface of the dielectric layer and the side faces of the barrier ribs.
Then, the front plate and the rear plate are faced with each other and sealed together so that the display electrode pairs are intersected with data electrodes. A discharge gas containing xenon having a partial pressure of 5% is charged into the inside discharge space. Discharge cells are formed in portions where the respective display electrode pairs are faced with the corresponding data electrodes. In a panel structured as above, gas discharge generates ultraviolet light in each discharge cell. This ultraviolet light excites the phosphors of red (R), green (G), and blue (G) so that the phosphors emit the respective colors for color display.
A general method of driving a panel is a sub-field method; one field period is divided into a plurality of sub-fields and combinations of light-emitting sub-fields provide gradation display.
Each sub-field has a setup period, an address period, and a sustain period. In the setup period, initializing discharge is generated to form, on the respective electrodes, wall charge necessary for the succeeding addressing operation. There are two kinds of initializing operations: an initializing operation for generating the initializing discharge in all the discharge cells (hereinafter abbreviated as “all-cell initializing operation”); and an initializing operation for generating the initializing discharge in the discharge cells having generated sustaining discharge therein (hereinafter “selective initializing operation”).
In the address period, addressing discharge is generated selectively in the discharge cells to be used to display an image, to form wall charge. Then, in the sustain period, alternately applying sustain pulses to the display electrode pairs each made of a scan electrode and a sustain electrode generates sustaining discharge in the discharge cells having generated addressing discharge therein, and causes the phosphor layers of the corresponding discharge cells to emit light. Thus, an image is displayed.
Among the sub-field methods, a novel driving method is disclosed. In this driving method, initializing discharge using a gradually changing voltage waveform and further selectively initializing the discharge cells having generated sustaining discharge therein minimize light emission unrelated to gradation display and improves the contrast ratio.
Specifically, among a plurality of sub-fields, the all-cell initializing operation for causing discharge in all the discharge cells is performed in the setup period in one sub-field, and the selective initializing operation for initializing only the discharge cells having generated the sustaining discharge therein is performed in the setup periods in the other sub-fields. As a result, light emission unrelated to display is only the light emission resulting from the discharge of the all-cell initializing operation. Thus, an image having high contrast can be displayed (see Patent Document 1, for example).
In such driving, the luminance of the area displaying a black picture (hereinafter abbreviated as “black picture level”) that changes depending on the light emission unrelated to the image display is only the weak light emission in the all-cell initializing operation. Thus, an image having high contrast can be displayed.
Further proposed as a technology for enhancing the visibility of an image by enhancing the luminance is to detect the average picture level (hereinafter “APL”) of input image signals and control the number of sustain pulses in the sustain period according to the APL (see Patent Document 2, for example).
The number of sustain pulses in each sub-field can be determined by multiplying a ratio of brightness at which the sub-field is to be displayed (hereinafter “brightness weight”) by a proportionality factor (hereinafter “luminance factor”). In this technology, the luminance factor is controlled according to an APL to determine the number of the sustain pulses in each sub-field. When an image signal has a high APL, the luminance factor is controlled to be small. When an image signal has a low APL, i.e., the entire image is dark, the luminance factor is controlled to be large. Such control can increase the luminance of a display image having a low APL and display a dark image brighter to enhance visibility of the image.
However, in recent years, larger panels with higher definition have been requiring higher contrast in the display images.    [Patent Document 1] Japanese Patent Unexamined Publication No. 2000-242224    [Patent Document 2] Japanese Patent Unexamined Publication No. H11-231825